The background of the invention will be set forth in two parts.
1. Field of the Invention
This invention relates to microwave tuned circuits, and more particularly to microwave resonant cavity structures.
2. Description of the Prior Art
Over the years, as higher and higher levels of RF energy have been generated at microwave frequencies, the problem of multipacting has become quite critical. Multipacting is an alternating current phenomenon most often brought about with conditions of relatively high RF power in a resonant cavity.
Under these conditions, a very high alternating field strength is set up in a confined volume representing a tuned resonance circuit. Here, any free electrons which happen to occupy this space will be strongly attached to a wall of the resonant structure where additional electrons will be "fired". Under this AC resonance condition, more and more free electrons will be produced from opposite walls of the cavity structure until an electron cloud is created. This is a classical secondary electron emission resonance phenomenon, and is the instigator of arcing within the resonant structure.
In the past, careful designing of the resonant cavity with respect to geometry less likely to provide arcing was utilized. However, with the now prevalent use of higher and higher RF powered resonant circuits being used in spacecraft, the problems have increased tremendously since molecular spacing, of air molecules, enters into the picture to enhance the possibilities of a secondary electron emission resonance phenomenon occurring. That is, in applications where continuous generation and/or amplification of relatively high RF microwave power is required as a spacecraft is launched and is subject to continuously decreasing air pressure, the molecular separation increases and may provide a critical condition where the molecules are at resonance within the cavity structure to enhance the electron cloud buildup and cause a spark to occur.
The standard "cure" in the past has been to seal the resonant structure so that the molecular separation remains constant in any pressure environment. However, this is costly in money, weight and bulk. It should, therefore, be evident that a resonant cavity system that was not subject to multipacting in any pressure environment and which does not require sealed and pressurized structures would constitute a significant advancement in the art.